1. Field of the Invention
The present invention relates to a recording head comprising a recording element substrate having recording elements formed thereon, and a driving element substrate having driving elements formed thereon for driving recording elements in accordance with a signal input from the outside, both substrates being welded under pressure, a head cartridge having the head, and a recording apparatus on which the head is mounted.
2. Related Background Art
FIGS. 1A and 1B are views showing one structural example of a recording element unit within a conventional recording head, wherein FIG. 1A is a schematic structural view, and FIG. 1B is a cross-sectional view taken along 1B--1B in FIG. 1A.
This conventional example is comprised of an HfB.sub.2 layer 1502 as a heating resistive layer for generating heat energy when electric current flows, a discrete electrode 1504 made of Al and a pattern electrode 1505 made of Al for supplying electric current to the HfB.sub.2 layer 1502 from the outside, a pattern wiring 1505b made of Al and a common electrode 1503 made of Al for allowing electric current supplied to the HfB.sub.2 layer 1502 to flow to the outside, a Ta layer 1508 as an anti-cavitation layer, an SiO.sub.2 layer 1506 as an oxidation resistant layer as well as an insulating layer, a photosensitive polyimide layer 1507 as an oxidation resistant layer as well as an insulating layer, and a holding member 1501 for holding each component as above cited, as shown in FIGS. 1A and 1B.
In the recording element unit as above constituted, if electric current for driving recording elements is caused to flow from the outside, the electric current will flow via the discrete electrode 1504 and the pattern wiring 1505a into the HfB.sub.2 layer 1502, and further via the pattern wiring 1505b and the common electrode 1503 to the outside, thereby generating heat energy in the HfB.sub.2 layer 1502. And liquid is discharged by heat energy generated to effect the recording on the recording medium.
When the HfB.sub.2 layer 1502, the discrete electrode 1504 and the pattern wirings 1505a, 1505b as above described are used in a combination (hereinafter referred to as a heating element), a plurality of heating elements are formed within one recording element unit in most cases, as shown in FIG. 1A.
Where a plurality of heating elements are provided within one recording elements unit, an ink jet recording apparatus for recording multiple dots simultaneously can be produced, thereby effecting the higher speed recording. Particularly, in recent years, the higher density and higher speed recording has been often demanded, and it is universal to perform the recording of one main scan line at a time, whereby a recording element unit having a number of heating elements arranged at high density has appeared.
As above described, when recording multiple dots simultaneously with a plurality of heating elements arranged within one recording element unit, each of the heating elements must be individually controlled to turn on or off. However, though means for effecting the ON/OFF control of heating elements (hereinafter referred to as driving elements) can be formed within the recording element unit, when the driving elements are formed on the same substrate as the recording elements within the recording unit, it is apprehended that the overall recording unit will not operate, if any of the recording elements and driving elements causes failure partly, whereby the driving elements are usually formed on a separate substrate (hereinafter referred to as a driving element substrate), which is then connected to the recording element unit.
A method of electrically connecting a substrate on which the recording elements are formed and a driving element substrate has been disclosed in Japanese Laid-Open Patent Application No. 3-121851.
That method as disclosed in Japanese Laid-Open Patent Application No. 3-121851 is one in which a bump-like electrode is formed to protrude on the substrate for the discrete electrode for the recording element having substantially the same constitution as shown in FIGS. 1A and 1B, the substrate having the recording elements formed and the driving element substrate being joined by press bonding.
Also, another method of connecting the substrate on which the recording elements are formed and the driving element substrate has been disclosed in Japanese Laid-Open Patent Application No. 1-302829.
FIGS. 2A to 2C are views for explaining a method of electrically connecting the recording element substrate and the driving element substrate as disclosed in Japanese Laid-Open Patent Application No. 1-302829.
In this conventional example as shown in FIGS. 2A and 2B, the driving element substrate 1705 having an electrode portion 1715 and an insulating membrane 1719 and the recording element substrate 1704 having an electrode portion 1714 and an insulating membrane 1720 are placed oppositely via an electrical connecting member 1703 with an electrically conductive member 1717 held by a holding member 1718 (FIG. 2A), and then press bonded (FIGS. 2B and 2C) to allow the recording element substrate 1704 and the driving element substrate 1705 to be joined together.
Note that the pitch of arranging the electrically conductive member 1717 is set to be narrower than the pitch of arranging the electrodes 1714 and 1715.
FIG. 3 is a perspective view showing one constitutional example of a recording head for an ink jet recording apparatus according to the background art, which comprises a recording element substrate and a driving element substrate press bonded together.
This conventional example is comprised of the driving element substrate 2002 on which driving elements 2003 are formed, the recording element substrate 2001 on which recording elements (not shown) are formed, a circuit substrate 2004 electrically connected to the driving element substrate 2002 by a method such as wire bonding, a sub-base board 2005 for pressing down the driving element substrate 2002 and the circuit substrate 2004, a press-bonding plate 2007 for press bonding the driving element substrate 2002 and the recording element substrate 2001 via the sub-base board 2005 for electrical connection therebetween, an elastic member 2008 provided between the press-bonding plate 2007 and the sub-base board 2005, a ceiling plate 2011 provided on a portion of the surface of the recording element substrate 2001 out of contact with the driving element substrate 2002, a main base board 2006 for securing the recording element substrate 2001 by adhesives to hold down each of the above-cited components, securing screws 2010 for securing the press-bonding plate 2007 and the sub-base board 2005, and spacers 2009, as shown in FIG. 3.
Also, an ink chamber (not shown) is disposed between the recording element substrate 2001 and the ceiling plate 2011, and supplied with energy for discharging the ink to the ink chamber by the recording elements on the recording element substrate 2001.
A way of positioning the recording element substrate and the driving element substrate in press bonding as shown in FIG. 3 will be described below.
FIGS. 4A and 4B are views for illustrating one example of the way of positioning the recording element substrate and the driving element substrate in press bonding as shown in FIG. 3.
In press bonding the recording element substrate and the driving element substrate, a positioning jig base board 2106 provided with locating pins 2103 for locating the recording element substrate 2001 and locating pins 2104 for locating the driving element substrate 2002 at respective predetermined positions is employed, as shown in FIGS. 4A and 4B.
First, the main base board 2006 is placed on the positioning jig base board 2106, and then the recording element substrate 2001 is pressed onto the main base board 2006 with the recording element substrate 2001 in abutment against the locating pins 2103, in which state the recording element substrate 2001 is secured onto the main base board 2006 by adhesives (FIG. 4A).
Then, the driving element substrate 2002 and the recording element substrate 2001 are press bonded, with the sub-base board 2005 having the driving element substrate 2002 and the circuit substrate 2004 positioned and secured together in abutment against the locating pins 2104, to make connection between the electrodes (not shown) on the driving element substrate 2002 and the electrodes (not shown) on the recording element substrate 2001 (FIG. 4B).
However, the following problems are found in the previously described background art.
(1) In press bonding the driving element substrate onto the recording element substrate, because the sub-base board onto which the driving element substrate is secured is too large, with its connection of the driving element substrate with the recording element substrate being at the end portion off the center of gravity for the sub-base board, it is difficult to take parallel balance in press bonding the driving element substrate onto the recording element substrate.
Therefore, the workability in press bonding the driving element substrate onto the recording element substrate is bad, and the reliability of the unit is reduced.
(2) In press bonding the driving element substrate onto the recording element substrate, because the sub-base board onto which the driving element substrate is secured is too large, and positioning the driving element substrate in the direction orthogonal to the array direction of recording elements is made at the end portion of the sub-base board farthest from the connection of the driving element substrate with the recording element substrate, the distance for positioning from the locating pins to the connection is longer, resulting in the greater distance error. Therefore, it is apprehended that the positional deviation of the connection arises.
(3) When the recording element substrate is exchanged by any cause such as failure, it must be exchanged along with the main base board bonded to the recording element substrate, giving rise to the increased costs of renewal parts.